Previous studies have implicated the benzodiazepine receptor in the sleep-inducing effects of these widely-used hypnotics, but the effector mechanism of this process is poorly understood. There is also in vitro evidence that benzodiazepines enhance calcium entry into synaptosomal preparations, leaving open the possibility that altered calcium flux may be involved in their actions. In order to explore this hypothesis, we administered intraventricular nifedipine, a calcium blocking agent. It was found that pretreatment with a dose of nifedipine which by itself does not affect sleep will prevent sleep-induction by flurazepam in rats. Effects on anticonvulsant properties of flurazepam were not apparent. This seems to suggest that changes in calcium channel function may be involved in the hypnotic action of benzodiazepines.